How to use the pyroute2.netns.setns function in pyroute2

def test_there_and_back(self):
        require_user('root')
        # wait until the previous test's side effects are gone
        time.sleep(2)
        #
        fd = open('/proc/self/ns/net', 'r')
        foo = str(uuid4())
        #
        # please notice, that IPRoute / IPDB, started in a netns, will continue
        # to work in a given netns even if the process changes to another netns
        #
        with IPRoute() as ip:
            links_main1 = set([x.get('index', None) for x in ip.get_links()])
        netnsmod.setns(foo)
        with IPRoute() as ip:
            links_foo = set([x.get('index', None) for x in ip.get_links()])
        netnsmod.setns(fd)
        with IPRoute() as ip:
            links_main2 = set([x.get('index', None) for x in ip.get_links()])
        assert links_main1 == links_main2
        assert links_main1 != links_foo
        netnsmod.remove(foo)
        fd.close()

ensures to move it back in original namespace or kills it if we fail to
    move back in original namespace.
    """
    if not namespace:
        yield
        return

    org_netns_fd = os.open(PROCESS_NETNS, os.O_RDONLY)
    pynetns.setns(namespace)
    try:
        yield
    finally:
        try:
            # NOTE(cby): this code is not executed only if we fail to
            # move in target namespace
            pynetns.setns(org_netns_fd)
        except Exception as e:
            msg = _('Failed to move back in original netns: %s') % e
            LOG.critical(msg)
            raise BackInNamespaceExit(msg)

def _enable_ipv6(netns):
    # Docker disables IPv6 for --net=none containers
    # TODO(apuimedo) remove when it is no longer the case
    try:
        netns = utils.convert_netns(netns)
        path = utils.convert_netns('/proc/self/ns/net')
        self_ns_fd = open(path)
        pyroute2.netns.setns(netns)
        path = utils.convert_netns('/proc/sys/net/ipv6/conf/all/disable_ipv6')
        with open(path, 'w') as disable_ipv6:
            disable_ipv6.write('0')
    except Exception:
        raise
    finally:
        pyroute2.netns.setns(self_ns_fd)

def _enable_ipv6(netns):
    # Docker disables IPv6 for --net=none containers
    # TODO(apuimedo) remove when it is no longer the case
    try:
        path = utils.convert_netns('/proc/self/ns/net')
        self_ns_fd = open(path)
        pyroute2.netns.setns(netns)
        path = utils.convert_netns('/proc/sys/net/ipv6/conf/all/disable_ipv6')
        with open(path, 'w') as disable_ipv6:
            disable_ipv6.write('0')
    except Exception:
        raise
    finally:
        pyroute2.netns.setns(self_ns_fd)

def Server(trnsp_in, trnsp_out, netns=None):

    def stop_server(signum, frame):
        Server.run = False

    Server.run = True
    signal.signal(signal.SIGTERM, stop_server)

    try:
        if netns is not None:
            netnsmod.setns(netns)
        ipr = IPRoute()
        lock = ipr._sproxy.lock
        ipr._s_channel = ProxyChannel(trnsp_out, 'broadcast')
    except Exception as e:
        trnsp_out.send({'stage': 'init',
                        'error': e})
        return 255

    inputs = [ipr.fileno(), trnsp_in.fileno()]
    broadcasts = {ipr.fileno(): ipr}
    outputs = []

    # all is OK so far
    trnsp_out.send({'stage': 'init',
                    'uname': config.uname,
                    'error': None})

def _enable_ipv6(netns):
    # Docker disables IPv6 for --net=none containers
    # TODO(apuimedo) remove when it is no longer the case
    try:
        netns = utils.convert_netns(netns)
        path = utils.convert_netns('/proc/self/ns/net')
        self_ns_fd = open(path)
        pyroute2.netns.setns(netns)
        path = utils.convert_netns('/proc/sys/net/ipv6/conf/all/disable_ipv6')
        with open(path, 'w') as disable_ipv6:
            disable_ipv6.write('0')
    except Exception:
        raise
    finally:
        pyroute2.netns.setns(self_ns_fd)